aDepartment of Chemistry, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249-0698, USA, and bDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia*Correspondence e-mail: edward.tiekink@gmail.com

(Received 24 November 2009;accepted 26 November 2009;online 4 December 2009)

In the title compound, C14H14N2O4, the central six-membered ring adopts a twisted boat conformation with the phenyl substituent occupying an orthogonal position [dihedral angle = 86.88 (11)°]. In the crystal, mol­ecules are linked by carboxylic acid–carbonyl O—H⋯O and amide–carbonyl N—H⋯O hydrogen bonds, forming a three-dimensional network.

The title compound (I), was prepared as a part of an on-going program aimed at developing water-soluble chiral auxiliaries (Mahindaratne et al., 2005a,b). The development of effective, water-soluble chiral auxiliaries is attractive from an environmental standpoint. We have been investigating the use of asparagine-derived auxiliaries for asymmetry transfer in Diels-Alder cycloadditions under aqueous conditions. Herein, we report the structure of the derivative (I), which was prepared upon cyclocondensation of L-asparagine under basic conditions with benzaldehyde followed by in situ acryloylation (Fig. 1). Precipitation occurred on addition of HCl and washing the precipitate with cold water yielded analytically pure acrylamide, (I).

The central ring in (I) adopts a twisted boat conformation, Fig. 2, whereby the RMS of the N1, N3, C4 and C6 atom is 0.057 Å with the C2 and C5 atoms lying 0.499 (3) and 0.612 (3) Å, respectively out of plane. The ring-puckering parameters are q2 = 0.653 (2) Å, q3 = -0.043 (2) Å, Q = 0.654 (2) Å, and ϕ2 = 49.76 (19)° (Cremer & Pople, 1975). The C21 substituents occupies an axial position whereas the C31, C41 and O6 substituents occupy equatorial positions. The phenyl ring occupies a position normal to the central ring as seen in the value of the dihedral angle between the two rings of 86.88 (11)°.

Two features are notable in the structure of (I). First, the crystal structure indicates the sole entrapment of the syn amide conformer of (I) (free acid of (II)-syn; Fig. 1). This is in contrast to the mixture of anti and syn conformers exhibited in aqueous sodium bicarbonate, in which anti conformer is favored by a ratio of 3:2 for (II) (sodium salt of (I)). The major conformer exhibited under these conditions was tentatively assigned as the anti conformer based on the stereochemistry of the major Diels-Alder product (2;S absolute configuration, Scheme 1), which is derived from the anti conformer of (II).

The crystal structure of (I) is stabilized by O–H···O and N–H···O hydrogen bonding, Table 1. Hydrogen bonds formed between the carboxylic acid-O41—H and carbonyl-O6 atoms leads to the formation of supramolecular chains aligned along the b axis, Fig. 3. The amide-N1—H hydrogen bonds to the carbonyl-O41 to form supramolecular chains aligned along the c axis, Fig. 4. Together, these hydrogen bonds consolidate molecules into a 3-D network, Fig. 5.

The H atoms were geometrically placed (O—H = 0.84 Å, N–H = 0.88 Å, and C—H = 0.95–1.00 Å) and refined as riding with Uiso(H) = 1.2–1.5Ueq(parent atom). In the absence of significant anomalous scattering effects, 1149 Friedel pairs were averaged in the final refinement. The absolute configuration was determined on the basis of the absolute stereochemistry of (S)-asparagine, a reagent employed in the synthesis.

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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